1. Field of the Invention
Embodiments of the present invention relate to a stringed instrument type electronic musical instrument (hereinafter referred to as an electronic stringed instrument) in which the string vibrations are converted to electrical signals and tones are generated based on the electrical signals. More particularly, embodiments of the present invention relate to a guitar synthesizer.
2. Description of Related Art
A typical electronic musical instrument in the form of a stringed instrument has strings. The electronic musical instrument of this type has a pickup device that detects string vibration and converts the vibration to electrical signals. The electronic musical instrument further includes an analog-to-digital converter that converts the electrical signals to digital signals that are digitally processed. The electronic musical instrument generates various musical tone data including data for pitch of each of the electrical signals, data for an envelope of vibration of each of the strings, data for starting time and attenuation of vibration of each of the strings and the like, based on the corresponding digital signals. Tones are generated based on the detected musical tone data. For example, such an electronic musical instrument is currently sold as a guitar synthesizer.
In the manner described above, a pitch and an envelope of each of the strings of the guitar synthesizer are detected and a musical tone is generated based on the detected pitch and envelope. Although the pitch and the envelope are typical parameters of string vibration, the guitar's original expression cannot be created merely by the pitch and the envelope of string vibration. In other words, the detected pitch and envelope alone do not generate a tone that is characteristic of the guitar.
For example, it is appreciated that a tone color generated by a string of the guitar varies depending upon where the string is picked. The closer to the bridge of the guitar a player picks the string, the more higher level overtones are generated, with the result that the tone color becomes "harder". On the other hand, the closer to the central area of the string and the farther from the bridge a player picks the string, the fewer higher level overtones are generated, with the result that the tone color becomes "soft". A tone generated based on the detected pitch and envelope alone does not reflect these characteristic features of the guitar.
Other conventional pitch detection methods are also used for detecting a pitch representative of a frequency of string vibration. For example, in the zero-cross detection method, the position at which an amplitude value of a waveshape intersects with a reference level value (the zero-cross point) is detected, and a time separation between two zero-cross points that corresponds to a cycle of the waveshape is measured. In still other conventional pitch detection methods, a cycle of a waveshape is obtained by calculating a self-correlation function of the waveshape, or by detecting a separation between peak values of the waveshape.
The above-described pitch detecting methods have both advantages and disadvantages. For example, when a string of a guitar is picked, the string starts vibrating. It is appreciated that the vibration of the string typically has a complicated waveshape during a period immediately after the string is picked. This starting period of the waveshape is called an attack portion and contains many higher level overtones. Therefore, it is difficult to detect the correct pitch during the attack portion and an erroneous pitch detection often occurs if pitch is detected during the attack portion.
In order to prevent an erroneous pitch detection, pitch detection may be delayed until the waveshape stabilizes to a specified level. However, in this case, since a pitch is not detected for some time after the string is picked, generation of a tone is delayed. As a result, a performer may feel that the tone generation is disordered and the delayed tone generation may adversely interfere with musical performance of the performer. For example, Japanese Laid-open Patent Application SHO 55-87196 describes a pitch detection method in which key-on data is outputted only when the same pitch is detected in two cycles. As a result, generation of a tone is delayed.